The invention relates generally to position sensors and, particularly, to a position sensor having a working air gap arranged relative to a magnetic field sensor such that the measuring sensitivity of the magnetic field sensor is perpendicular to the shifting direction of the magnet.
U.S. Pat. No. 5,532,585, the entire disclosure of which is incorporated herein by reference, discloses a position sensor in which a permanent magnet is linearly shifted in a primary air gap between ferromagnetic flux-concentrating pieces. A working air gap, perpendicular to the primary air gap, is present between two flux-concentrating pieces. In this instance, the working air gap features a magnetic field sensor in the form of a Hall probe, the direction of sensitivity of which is parallel to the shifting direction of the magnet.
When using a sliding position sensor having a Hall-effect probe, care must be taken to prevent the interfering influence of foreign magnetic fields that invalidate the measurement result. For example, suitable shielding measures may be undertaken to prevent this interference. However, if a position sensor must be connected to an electromagnetic actuator to form a compact unit, shielding measures are often not sufficient or are very costly.
Such a situation occurs, for instance, when using a position sensor together with a solenoid. One such example is the regulation of a valve in the exhaust gas recirculation system of an internal combustion engine. In this connection, the solenoid may produce an axial interference field that may assume significant values, particularly along the axis of symmetry. For the aforementioned position sensor, such an axial interference field may have an effect on the Hall-effect probe and consequently invalidate the measurement result.
For these reasons, a position sensor of the aforementioned type is needed that is insensitive to the greatest possible extent to magnetic interference fields, particularly those acting coaxial with the shifting direction.
The invention meets the above needs and overcomes the deficiencies of the prior art by providing an improved position sensor. Among the several objects of this invention may be noted the provision of a position sensor that largely eliminates the influence of axial magnetic interference fields.
According to a refinement of the invention, the flux-concentrating pieces are developed to be symmetrical with the primary air gap and working air gap. The primary and working air gap are preferably located in the same plane. The effective area of the working air gap is preferably smaller than the effective area of the primary air gap, allowing the utilized magnetic flux density to be increased in the working gap.
According to a refinement of the invention, two generally equal pairs of flux-concentrating pieces are arranged in succession in the shifting direction. Each pair of flux-concentrating pieces forms a magnetic circuit. The two magnetic circuits formed in this way are magnetically coupled by means of a coupling gap. Preferably, a magnetic field sensor, which preferably is a Hall-effect probe, is arranged in each magnetic circuit. If a magnet is located essentially completely in the primary air gap of a first pair of flux-concentrating pieces, then in this position, the magnetic flux density is at a maximum in the working gap of this pair of flux-concentrating pieces and at a minimum in the working gap of the other pair of flux-concentrating pieces. The aforementioned magnetic coupling of the two magnetic circuits by the coupling gap is responsible for the presence of a nonzero flux density in the second working gap. If the magnet is shifted successively from the primary air gap of the first pair of flux-concentrating pieces into that of the second, then the flux density increases in the second working gap and decreases in the first. By dimensioning the geometric measurements, the most linear path possible for the Hall voltage may be achieved as a function of the shifting path.
Briefly described, a position sensor embodying aspects of the invention includes ferromagnetic flux-concentrating pieces defining a primary air gap and a working air gap between the pieces. A permanent magnet, which is movable along a shifting direction, is positioned in the primary air gap between the flux-concentrating pieces. The position sensor also includes a magnetic field sensor positioned in the working air gap between the flux-concentrating pieces. The magnetic field sensor is arranged relative to the working air gap so that its direction of measuring sensitivity is substantially perpendicular to the shifting direction of the magnet.
In another embodiment, a position sensor according to the invention has first and second pairs of ferromagnetic flux-concentrating pieces. Each pair of flux-concentrating pieces defines a primary air gap and a corresponding working air gap between the pieces. Each primary air gap is separated from its corresponding working air gap. A permanent magnet, which is movable along a shifting direction, is positioned in the primary air gaps between the flux-concentrating pieces. The first and second pairs of flux-concentrating pieces are arranged so that the permanent magnet is movable within the primary air gap of each pair of flux-concentrating pieces. The position sensor also includes a magnetic field sensor positioned in the working air gap between each pair of flux-concentrating pieces. Each magnetic field sensor is arranged relative to the respective working air gap so that its direction of measuring sensitivity is substantially perpendicular to the shifting direction of the permanent magnet.
Alternatively, the invention may comprise various other methods and systems.
Other objects and features will be in part apparent and in part pointed out hereinafter.